/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineTournamentInterface.h
It is valid to request Team IDs or Player IDs from a Team tournament, and it is only valid to request Player IDs from an Individual tournament.
void QueryParticipantList ( const FUniqueNetIdRef UserId, const [FOnlineTournamentIdRef](API\Plugins\OnlineSubsystem\Interfaces\FOnlineTournamentIdRef) TournamentId, const [FOnlineTournamentParticipantQueryFilter](API\Plugins\OnlineSubsystem\Interfaces\FOnlineTournamentParticipantQuer-) & QueryFilter, const [FOnlineTournamentQueryParticipantListComplete](API\Plugins\OnlineSubsystem\Interfaces\FOnlineTournamen-_2) & Delegate )